Retinal neovascularization is the leading cause of blindness in the United States among working-age adults (diabetic retinopathy) and infants (retinopathy of prematurity). Choroidal neovascularization occurs in cases of age-related macular degeneration, the most common cause of blindness in individuals over the age of 60. Although the exact mechanisms leading to the development of new vessels in retinal and choroidal angiogenesis may be different and poorly understood, a common event in both cases is the breakdown of the capillary basement membrane and the invasion and migration of microvascular endothelial cells through the extracellular matrix. The process of angiogenesis is dependent upon the expression of the serine proteinase urokinase and its receptor as well as specific members of the matrix metalloproteinase (MMP) family of enzymes. Understanding the mechanisms of proteinase expression and identifying inhibitors of their function may therefore provide unique opportunities for the development of therapeutic interventions for retinal and choroidal neovascularization. This application will test the hypothesis that retinal and subretinal neovascularization is facilitated by the expression of specific extracelluar proteinases, the inhibition of which may lead to new and useful therapies. The aims of this study which will address the hypothesis are (1) To further characterize the role of extracellular proteinases and their inhibitors in well established models of retinal and choroidal neovascularization. We will use biochemical, histological and molecular techniques, including the use of knockout animals, to address this aim. (2) To determine the factors and mechanisms which regulate the expression of proteinases in the retina and choroid. Studies will focus on the role of tumor necrosis factor alpha (TNFalpha) and angiopoietin 2 (Ang2) in the regulation of proteinase expression, alone or in combination with other growth factors and a hypoxic stimulus. (3) To determine if the extent of retinal and choroidal neovascularization can be reduced through the use of specific compounds which directly or indirectly affect proteinase expression and/or activity. The results of these studies will allow us to further define the mechanisms involved in the formation of new vessels in the retina and choroid which can lead to serious visual complications, and whether a specific stage of the angiogenic process is an appropriate target for therapeutic intervention. Such an approach will provide a rational basis for the development of potentially powerful and effective therapeutics for ocular neovascularization.